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- //===----------------------------------------------------------------------===//
- //
- // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
- // See https://llvm.org/LICENSE.txt for license information.
- // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
- //
- //
- // Darwin's alternative to DWARF based unwind encodings.
- //
- //===----------------------------------------------------------------------===//
- #ifndef __COMPACT_UNWIND_ENCODING__
- #define __COMPACT_UNWIND_ENCODING__
- #include <stdint.h>
- //
- // Compilers can emit standard DWARF FDEs in the __TEXT,__eh_frame section
- // of object files. Or compilers can emit compact unwind information in
- // the __LD,__compact_unwind section.
- //
- // When the linker creates a final linked image, it will create a
- // __TEXT,__unwind_info section. This section is a small and fast way for the
- // runtime to access unwind info for any given function. If the compiler
- // emitted compact unwind info for the function, that compact unwind info will
- // be encoded in the __TEXT,__unwind_info section. If the compiler emitted
- // DWARF unwind info, the __TEXT,__unwind_info section will contain the offset
- // of the FDE in the __TEXT,__eh_frame section in the final linked image.
- //
- // Note: Previously, the linker would transform some DWARF unwind infos into
- // compact unwind info. But that is fragile and no longer done.
- //
- // The compact unwind encoding is a 32-bit value which encoded in an
- // architecture specific way, which registers to restore from where, and how
- // to unwind out of the function.
- //
- typedef uint32_t compact_unwind_encoding_t;
- // architecture independent bits
- enum {
- UNWIND_IS_NOT_FUNCTION_START = 0x80000000,
- UNWIND_HAS_LSDA = 0x40000000,
- UNWIND_PERSONALITY_MASK = 0x30000000,
- };
- //
- // x86
- //
- // 1-bit: start
- // 1-bit: has lsda
- // 2-bit: personality index
- //
- // 4-bits: 0=old, 1=ebp based, 2=stack-imm, 3=stack-ind, 4=DWARF
- // ebp based:
- // 15-bits (5*3-bits per reg) register permutation
- // 8-bits for stack offset
- // frameless:
- // 8-bits stack size
- // 3-bits stack adjust
- // 3-bits register count
- // 10-bits register permutation
- //
- enum {
- UNWIND_X86_MODE_MASK = 0x0F000000,
- UNWIND_X86_MODE_EBP_FRAME = 0x01000000,
- UNWIND_X86_MODE_STACK_IMMD = 0x02000000,
- UNWIND_X86_MODE_STACK_IND = 0x03000000,
- UNWIND_X86_MODE_DWARF = 0x04000000,
- UNWIND_X86_EBP_FRAME_REGISTERS = 0x00007FFF,
- UNWIND_X86_EBP_FRAME_OFFSET = 0x00FF0000,
- UNWIND_X86_FRAMELESS_STACK_SIZE = 0x00FF0000,
- UNWIND_X86_FRAMELESS_STACK_ADJUST = 0x0000E000,
- UNWIND_X86_FRAMELESS_STACK_REG_COUNT = 0x00001C00,
- UNWIND_X86_FRAMELESS_STACK_REG_PERMUTATION = 0x000003FF,
- UNWIND_X86_DWARF_SECTION_OFFSET = 0x00FFFFFF,
- };
- enum {
- UNWIND_X86_REG_NONE = 0,
- UNWIND_X86_REG_EBX = 1,
- UNWIND_X86_REG_ECX = 2,
- UNWIND_X86_REG_EDX = 3,
- UNWIND_X86_REG_EDI = 4,
- UNWIND_X86_REG_ESI = 5,
- UNWIND_X86_REG_EBP = 6,
- };
- //
- // For x86 there are four modes for the compact unwind encoding:
- // UNWIND_X86_MODE_EBP_FRAME:
- // EBP based frame where EBP is push on stack immediately after return address,
- // then ESP is moved to EBP. Thus, to unwind ESP is restored with the current
- // EPB value, then EBP is restored by popping off the stack, and the return
- // is done by popping the stack once more into the pc.
- // All non-volatile registers that need to be restored must have been saved
- // in a small range in the stack that starts EBP-4 to EBP-1020. The offset/4
- // is encoded in the UNWIND_X86_EBP_FRAME_OFFSET bits. The registers saved
- // are encoded in the UNWIND_X86_EBP_FRAME_REGISTERS bits as five 3-bit entries.
- // Each entry contains which register to restore.
- // UNWIND_X86_MODE_STACK_IMMD:
- // A "frameless" (EBP not used as frame pointer) function with a small
- // constant stack size. To return, a constant (encoded in the compact
- // unwind encoding) is added to the ESP. Then the return is done by
- // popping the stack into the pc.
- // All non-volatile registers that need to be restored must have been saved
- // on the stack immediately after the return address. The stack_size/4 is
- // encoded in the UNWIND_X86_FRAMELESS_STACK_SIZE (max stack size is 1024).
- // The number of registers saved is encoded in UNWIND_X86_FRAMELESS_STACK_REG_COUNT.
- // UNWIND_X86_FRAMELESS_STACK_REG_PERMUTATION contains which registers were
- // saved and their order.
- // UNWIND_X86_MODE_STACK_IND:
- // A "frameless" (EBP not used as frame pointer) function large constant
- // stack size. This case is like the previous, except the stack size is too
- // large to encode in the compact unwind encoding. Instead it requires that
- // the function contains "subl $nnnnnnnn,ESP" in its prolog. The compact
- // encoding contains the offset to the nnnnnnnn value in the function in
- // UNWIND_X86_FRAMELESS_STACK_SIZE.
- // UNWIND_X86_MODE_DWARF:
- // No compact unwind encoding is available. Instead the low 24-bits of the
- // compact encoding is the offset of the DWARF FDE in the __eh_frame section.
- // This mode is never used in object files. It is only generated by the
- // linker in final linked images which have only DWARF unwind info for a
- // function.
- //
- // The permutation encoding is a Lehmer code sequence encoded into a
- // single variable-base number so we can encode the ordering of up to
- // six registers in a 10-bit space.
- //
- // The following is the algorithm used to create the permutation encoding used
- // with frameless stacks. It is passed the number of registers to be saved and
- // an array of the register numbers saved.
- //
- //uint32_t permute_encode(uint32_t registerCount, const uint32_t registers[6])
- //{
- // uint32_t renumregs[6];
- // for (int i=6-registerCount; i < 6; ++i) {
- // int countless = 0;
- // for (int j=6-registerCount; j < i; ++j) {
- // if ( registers[j] < registers[i] )
- // ++countless;
- // }
- // renumregs[i] = registers[i] - countless -1;
- // }
- // uint32_t permutationEncoding = 0;
- // switch ( registerCount ) {
- // case 6:
- // permutationEncoding |= (120*renumregs[0] + 24*renumregs[1]
- // + 6*renumregs[2] + 2*renumregs[3]
- // + renumregs[4]);
- // break;
- // case 5:
- // permutationEncoding |= (120*renumregs[1] + 24*renumregs[2]
- // + 6*renumregs[3] + 2*renumregs[4]
- // + renumregs[5]);
- // break;
- // case 4:
- // permutationEncoding |= (60*renumregs[2] + 12*renumregs[3]
- // + 3*renumregs[4] + renumregs[5]);
- // break;
- // case 3:
- // permutationEncoding |= (20*renumregs[3] + 4*renumregs[4]
- // + renumregs[5]);
- // break;
- // case 2:
- // permutationEncoding |= (5*renumregs[4] + renumregs[5]);
- // break;
- // case 1:
- // permutationEncoding |= (renumregs[5]);
- // break;
- // }
- // return permutationEncoding;
- //}
- //
- //
- // x86_64
- //
- // 1-bit: start
- // 1-bit: has lsda
- // 2-bit: personality index
- //
- // 4-bits: 0=old, 1=rbp based, 2=stack-imm, 3=stack-ind, 4=DWARF
- // rbp based:
- // 15-bits (5*3-bits per reg) register permutation
- // 8-bits for stack offset
- // frameless:
- // 8-bits stack size
- // 3-bits stack adjust
- // 3-bits register count
- // 10-bits register permutation
- //
- enum {
- UNWIND_X86_64_MODE_MASK = 0x0F000000,
- UNWIND_X86_64_MODE_RBP_FRAME = 0x01000000,
- UNWIND_X86_64_MODE_STACK_IMMD = 0x02000000,
- UNWIND_X86_64_MODE_STACK_IND = 0x03000000,
- UNWIND_X86_64_MODE_DWARF = 0x04000000,
- UNWIND_X86_64_RBP_FRAME_REGISTERS = 0x00007FFF,
- UNWIND_X86_64_RBP_FRAME_OFFSET = 0x00FF0000,
- UNWIND_X86_64_FRAMELESS_STACK_SIZE = 0x00FF0000,
- UNWIND_X86_64_FRAMELESS_STACK_ADJUST = 0x0000E000,
- UNWIND_X86_64_FRAMELESS_STACK_REG_COUNT = 0x00001C00,
- UNWIND_X86_64_FRAMELESS_STACK_REG_PERMUTATION = 0x000003FF,
- UNWIND_X86_64_DWARF_SECTION_OFFSET = 0x00FFFFFF,
- };
- enum {
- UNWIND_X86_64_REG_NONE = 0,
- UNWIND_X86_64_REG_RBX = 1,
- UNWIND_X86_64_REG_R12 = 2,
- UNWIND_X86_64_REG_R13 = 3,
- UNWIND_X86_64_REG_R14 = 4,
- UNWIND_X86_64_REG_R15 = 5,
- UNWIND_X86_64_REG_RBP = 6,
- };
- //
- // For x86_64 there are four modes for the compact unwind encoding:
- // UNWIND_X86_64_MODE_RBP_FRAME:
- // RBP based frame where RBP is push on stack immediately after return address,
- // then RSP is moved to RBP. Thus, to unwind RSP is restored with the current
- // EPB value, then RBP is restored by popping off the stack, and the return
- // is done by popping the stack once more into the pc.
- // All non-volatile registers that need to be restored must have been saved
- // in a small range in the stack that starts RBP-8 to RBP-2040. The offset/8
- // is encoded in the UNWIND_X86_64_RBP_FRAME_OFFSET bits. The registers saved
- // are encoded in the UNWIND_X86_64_RBP_FRAME_REGISTERS bits as five 3-bit entries.
- // Each entry contains which register to restore.
- // UNWIND_X86_64_MODE_STACK_IMMD:
- // A "frameless" (RBP not used as frame pointer) function with a small
- // constant stack size. To return, a constant (encoded in the compact
- // unwind encoding) is added to the RSP. Then the return is done by
- // popping the stack into the pc.
- // All non-volatile registers that need to be restored must have been saved
- // on the stack immediately after the return address. The stack_size/8 is
- // encoded in the UNWIND_X86_64_FRAMELESS_STACK_SIZE (max stack size is 2048).
- // The number of registers saved is encoded in UNWIND_X86_64_FRAMELESS_STACK_REG_COUNT.
- // UNWIND_X86_64_FRAMELESS_STACK_REG_PERMUTATION contains which registers were
- // saved and their order.
- // UNWIND_X86_64_MODE_STACK_IND:
- // A "frameless" (RBP not used as frame pointer) function large constant
- // stack size. This case is like the previous, except the stack size is too
- // large to encode in the compact unwind encoding. Instead it requires that
- // the function contains "subq $nnnnnnnn,RSP" in its prolog. The compact
- // encoding contains the offset to the nnnnnnnn value in the function in
- // UNWIND_X86_64_FRAMELESS_STACK_SIZE.
- // UNWIND_X86_64_MODE_DWARF:
- // No compact unwind encoding is available. Instead the low 24-bits of the
- // compact encoding is the offset of the DWARF FDE in the __eh_frame section.
- // This mode is never used in object files. It is only generated by the
- // linker in final linked images which have only DWARF unwind info for a
- // function.
- //
- // ARM64
- //
- // 1-bit: start
- // 1-bit: has lsda
- // 2-bit: personality index
- //
- // 4-bits: 4=frame-based, 3=DWARF, 2=frameless
- // frameless:
- // 12-bits of stack size
- // frame-based:
- // 4-bits D reg pairs saved
- // 5-bits X reg pairs saved
- // DWARF:
- // 24-bits offset of DWARF FDE in __eh_frame section
- //
- enum {
- UNWIND_ARM64_MODE_MASK = 0x0F000000,
- UNWIND_ARM64_MODE_FRAMELESS = 0x02000000,
- UNWIND_ARM64_MODE_DWARF = 0x03000000,
- UNWIND_ARM64_MODE_FRAME = 0x04000000,
- UNWIND_ARM64_FRAME_X19_X20_PAIR = 0x00000001,
- UNWIND_ARM64_FRAME_X21_X22_PAIR = 0x00000002,
- UNWIND_ARM64_FRAME_X23_X24_PAIR = 0x00000004,
- UNWIND_ARM64_FRAME_X25_X26_PAIR = 0x00000008,
- UNWIND_ARM64_FRAME_X27_X28_PAIR = 0x00000010,
- UNWIND_ARM64_FRAME_D8_D9_PAIR = 0x00000100,
- UNWIND_ARM64_FRAME_D10_D11_PAIR = 0x00000200,
- UNWIND_ARM64_FRAME_D12_D13_PAIR = 0x00000400,
- UNWIND_ARM64_FRAME_D14_D15_PAIR = 0x00000800,
- UNWIND_ARM64_FRAMELESS_STACK_SIZE_MASK = 0x00FFF000,
- UNWIND_ARM64_DWARF_SECTION_OFFSET = 0x00FFFFFF,
- };
- // For arm64 there are three modes for the compact unwind encoding:
- // UNWIND_ARM64_MODE_FRAME:
- // This is a standard arm64 prolog where FP/LR are immediately pushed on the
- // stack, then SP is copied to FP. If there are any non-volatile registers
- // saved, then are copied into the stack frame in pairs in a contiguous
- // range right below the saved FP/LR pair. Any subset of the five X pairs
- // and four D pairs can be saved, but the memory layout must be in register
- // number order.
- // UNWIND_ARM64_MODE_FRAMELESS:
- // A "frameless" leaf function, where FP/LR are not saved. The return address
- // remains in LR throughout the function. If any non-volatile registers
- // are saved, they must be pushed onto the stack before any stack space is
- // allocated for local variables. The stack sized (including any saved
- // non-volatile registers) divided by 16 is encoded in the bits
- // UNWIND_ARM64_FRAMELESS_STACK_SIZE_MASK.
- // UNWIND_ARM64_MODE_DWARF:
- // No compact unwind encoding is available. Instead the low 24-bits of the
- // compact encoding is the offset of the DWARF FDE in the __eh_frame section.
- // This mode is never used in object files. It is only generated by the
- // linker in final linked images which have only DWARF unwind info for a
- // function.
- //
- ////////////////////////////////////////////////////////////////////////////////
- //
- // Relocatable Object Files: __LD,__compact_unwind
- //
- ////////////////////////////////////////////////////////////////////////////////
- //
- // A compiler can generated compact unwind information for a function by adding
- // a "row" to the __LD,__compact_unwind section. This section has the
- // S_ATTR_DEBUG bit set, so the section will be ignored by older linkers.
- // It is removed by the new linker, so never ends up in final executables.
- // This section is a table, initially with one row per function (that needs
- // unwind info). The table columns and some conceptual entries are:
- //
- // range-start pointer to start of function/range
- // range-length
- // compact-unwind-encoding 32-bit encoding
- // personality-function or zero if no personality function
- // lsda or zero if no LSDA data
- //
- // The length and encoding fields are 32-bits. The other are all pointer sized.
- //
- // In x86_64 assembly, these entry would look like:
- //
- // .section __LD,__compact_unwind,regular,debug
- //
- // #compact unwind for _foo
- // .quad _foo
- // .set L1,LfooEnd-_foo
- // .long L1
- // .long 0x01010001
- // .quad 0
- // .quad 0
- //
- // #compact unwind for _bar
- // .quad _bar
- // .set L2,LbarEnd-_bar
- // .long L2
- // .long 0x01020011
- // .quad __gxx_personality
- // .quad except_tab1
- //
- //
- // Notes: There is no need for any labels in the __compact_unwind section.
- // The use of the .set directive is to force the evaluation of the
- // range-length at assembly time, instead of generating relocations.
- //
- // To support future compiler optimizations where which non-volatile registers
- // are saved changes within a function (e.g. delay saving non-volatiles until
- // necessary), there can by multiple lines in the __compact_unwind table for one
- // function, each with a different (non-overlapping) range and each with
- // different compact unwind encodings that correspond to the non-volatiles
- // saved at that range of the function.
- //
- // If a particular function is so wacky that there is no compact unwind way
- // to encode it, then the compiler can emit traditional DWARF unwind info.
- // The runtime will use which ever is available.
- //
- // Runtime support for compact unwind encodings are only available on 10.6
- // and later. So, the compiler should not generate it when targeting pre-10.6.
- ////////////////////////////////////////////////////////////////////////////////
- //
- // Final Linked Images: __TEXT,__unwind_info
- //
- ////////////////////////////////////////////////////////////////////////////////
- //
- // The __TEXT,__unwind_info section is laid out for an efficient two level lookup.
- // The header of the section contains a coarse index that maps function address
- // to the page (4096 byte block) containing the unwind info for that function.
- //
- #define UNWIND_SECTION_VERSION 1
- struct unwind_info_section_header
- {
- uint32_t version; // UNWIND_SECTION_VERSION
- uint32_t commonEncodingsArraySectionOffset;
- uint32_t commonEncodingsArrayCount;
- uint32_t personalityArraySectionOffset;
- uint32_t personalityArrayCount;
- uint32_t indexSectionOffset;
- uint32_t indexCount;
- // compact_unwind_encoding_t[]
- // uint32_t personalities[]
- // unwind_info_section_header_index_entry[]
- // unwind_info_section_header_lsda_index_entry[]
- };
- struct unwind_info_section_header_index_entry
- {
- uint32_t functionOffset;
- uint32_t secondLevelPagesSectionOffset; // section offset to start of regular or compress page
- uint32_t lsdaIndexArraySectionOffset; // section offset to start of lsda_index array for this range
- };
- struct unwind_info_section_header_lsda_index_entry
- {
- uint32_t functionOffset;
- uint32_t lsdaOffset;
- };
- //
- // There are two kinds of second level index pages: regular and compressed.
- // A compressed page can hold up to 1021 entries, but it cannot be used
- // if too many different encoding types are used. The regular page holds
- // 511 entries.
- //
- struct unwind_info_regular_second_level_entry
- {
- uint32_t functionOffset;
- compact_unwind_encoding_t encoding;
- };
- #define UNWIND_SECOND_LEVEL_REGULAR 2
- struct unwind_info_regular_second_level_page_header
- {
- uint32_t kind; // UNWIND_SECOND_LEVEL_REGULAR
- uint16_t entryPageOffset;
- uint16_t entryCount;
- // entry array
- };
- #define UNWIND_SECOND_LEVEL_COMPRESSED 3
- struct unwind_info_compressed_second_level_page_header
- {
- uint32_t kind; // UNWIND_SECOND_LEVEL_COMPRESSED
- uint16_t entryPageOffset;
- uint16_t entryCount;
- uint16_t encodingsPageOffset;
- uint16_t encodingsCount;
- // 32-bit entry array
- // encodings array
- };
- #define UNWIND_INFO_COMPRESSED_ENTRY_FUNC_OFFSET(entry) (entry & 0x00FFFFFF)
- #define UNWIND_INFO_COMPRESSED_ENTRY_ENCODING_INDEX(entry) ((entry >> 24) & 0xFF)
- #endif
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